284 ERNEST WARREN. 



The Development of D. cireigerum in the Crayfish. 



The Fjgg. — Tlie eggs are very small^ and pass out from 

 the uterus into the space between the body and the cyst-Avall. 

 The encysted animal appears to die after the formation of the 

 eggs, and the cyst-wall ultimately breaks and liberates the 

 eggs. 



The egg-shell is thin and of a dark brown colour; it is very 

 frequently flattened, and shaped like a convexo-concave lens, 

 which is perhaps due to shrinkage ; its average length is 

 •012 mm,, and breadth '008 mm. Viewed from the convex or 

 concave surface, or even in edge view, the egg is seen to 

 taper towards one end where there occurs a dark-coloured 

 thickened nodule. At the other end, which is rounded, there 

 can be seen the operculum which is doubtless pushed out 

 when the embryo hatches (Fig. XI, 1). 



Inside the egg-shell there can be distinguished the egg- 

 cell with a somewhat irregular outline, and surrounding it 

 are a dozen or more yolk-cells containing globules of yolk. 



Segmentation. — The egg-cell divides into a number of 

 blastomeres (fig. 2), and at the same time the yolk is gradu- 

 ally extracted from the yolk-cells, which soon appear as flat- 

 tened cells between the large spherical blastomeres. The 

 nuclei of the blastomeres only stain with great difficulty, while 

 the flattened nuclei of the yolk-cells stain very readily. In 

 this condition the embryo apparently emerges from the egg- 

 shell, but I have not seen an embryo in the act of hatching. 



iSporocyst Stage. — The embryo, Avliich may now be 

 termed a sporocyst, consisting of a few quite irregularly 

 arranged blastomeres and flattened yolk-cells, works its way 

 into the thin sheets of connective tissue around the muscles, 

 testis, nerve-cord, etc., and it may acquire a slightly reddish 

 or brownish tint (fig. 3). 



The sporocyst, which is generally more or less s])herical, now 

 grows considerably, and it may send out many buds consisting 

 of one or several blastomeres. Some of these buds mav be- 



